seismic performance of silty soil sites - sacramento...

Seismic Performance of Silty Soil Sites

Jonathan Bray, Ph.D., P.E., NAE, & Christine Beyzaei, Ph.D., P.E.Univ. of California, Berkeley

With Contributions From: M. Cubrinovski, M. Riemer, C. Markham, J. Zupan, M. Stringer,

S. van Ballegooy, M. Jacka, R. Wentz, etc.

Sponsors: National Science Foundation, Pacific Earthquake Engineering Research Center,Ministry of Business, Innovation & Employment, and Earthquake Commission New Zealand

LIQUEFACTION

1964 Niigata, Japan EQ (from H.B. Seed)1906 San Francisco EQ (Lawson et al. 1908)

1989 Loma Prieta EQ

EFFECTS

LIQUEFACTION EFFECTS

Flow Liquefaction Cyclic Mobility(strain-softening large strain) (strain-hardening limited strain)

FS =1.2

FS =1.2

LIQUEFACTION EFFECTS

Idriss & Boulanger 2008

Flow Liquefaction

Cyclic Mobility

85

LiquefactionEffects Observed at Ground Surface

No LiquefactionEffects Observed at Ground Surface

FS = CRR / CSR

CRR

CSR

Liquefaction Flow Slides when qc1Ncs-Sr < 85


85

New Zealand

Pacific plate

Australianplate

Alpine FaultMCE Mw = 8

Christchurch

Wellington

MW = 7.14 Sept 10

MW = 6.013 June 11

MW = 6.222 Feb 11

MW = 5.923 Dec 11

2010-2011 Canterbury Earthquake Sequence

GNS Science

Canterbury NZ EQs: Widespread Liquefaction

Cubrinovski et al. 2011

Liquefaction Effects in Christchurch

From M. Cubrinovski

Liquefaction from 3+ EQs (Cubrinovski 2011)

Base Map – 22 Feb 2011 – Mw = 6.2White Areas – 4 Sep 2010 – Mw = 7.1Black Areas – 13 Jun 2011 – Mw = 6.0

CBD

4 Sept 2010

(Mark Quigley: Avonside)

22 Feb 2011

16 April 2011

13 June 2011: Part 1

13 June 2011: Part 2

Repeated Liquefaction Events

Age of Christchurch Soils

from M. Cubrinovski

After Liquefaction

0

Liquefaction in Christchurch

(van Ballegooy et al. 2014)

Capturing Liquefaction Effects

Post-Liquefaction Volumetric Strain (εv)

Ishihara & Yoshimine 1992

Post-Liquefaction Volumetric Strain (εv)

Ishihara & Yoshimine 1992

Decreasing FS In

crea

sing

ε v

Dec

reas

ing

Dr


van Ballegooy et al. 2014

LSN considers when FS > 1

LSN limited by max εv

LSN affected by Dr

LSN weights heavily shallow layers


van Ballegooy et al. 2014

Liquefaction in Christchurch


LSNEstimates

LandDamage


2010 Darfield EQ

Ejecta Observed

No Ejecta

van Ballegooy et al.Tonkin & Taylor

for the EQC

Ic = 1.8

qc (MPa) Ic

Dep

th (m

)

Observations of Liquefaction Ejecta

CPTProfiles

Increasing PGA

Increasing Manifestations

Beyzaei et al.

Liquefaction of Silty Soil Sites

site where no liquefaction effects were observed;yet simplified procedures indicate liquefaction was expected

(from R. Wentz, Wentz-Pacific)

Site 23

Liquefaction Assessment at Stratified Site

Riccarton Road Site 23 22 Feb 2011 EQ: PGA = 0.37 g, GWT = 0.6 m BGS, PL=50%, LPI = 19, CPT_36420 (Beyzaei et al.; CRR and FS plots exported from CLiq)

CRR & CSR

0.0 0.1 0.2 0.3 0.4 0.5

DEPT

H BE

LOW

GRO

UND

SURF

ACE

(m)

0

1

2

3

4

5

6

7

8

9

10

Factor of Safety

0.0 0.5 1.0 1.5 2.0

Settlement (cm)

0 3 6 9 12 15

GWT GWT GWT

CRR

CSR

Settlement ~ 13 cmLSN = 29

BUT no liquefaction effects observed

Cyclic Triaxial Testing Program

DIAMETER (m)

0.1 1 10 100 1000 10000

PER

CEN

T FI

NER

(%)

0

20

40

60

80

100

Site 21Site 23Site 33 (silty soil)Site 33 (sand)S33-DM1-5U-B (top)S33-DM1-5U-B (mid)S33-DM1-5U-B (bot)

S33-DM1-6U-B (ends)S33-DM1-6U-B (mid)S21-DM1-3U-BS23-DM1-3U-AS23-DM1-7U-BEQC-4

Range of silty soils tested

Beyzaei et al.

Cyclic Triaxial Test Results

Axial Strain (%)-5 -4 -3 -2 -1 0 1 2 3 4 5

q/(2

p'0)

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

Axial Strain (%)-5 -4 -3 -2 -1 0 1 2 3 4 5

q/(2

p'0)

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6(a) Cycle 1 (b) Cycle 2

Axial Strain (%)-5 -4 -3 -2 -1 0 1 2 3 4 5

q/(2

p'0)

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

Axial Strain (%)-5 -4 -3 -2 -1 0 1 2 3 4 5

q/(2

p'0)

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

EQC4-DM1B-7U-A (Clean Sand)S21-DM1-3U-A (Silt, NP)

S33-DM1-8U-A (Silt, PI=10)S33-DM1-8U-B (Silt, PI=10)

(c) 3% SA (d) 5% DA

Beyzaei et al.

Liquefaction Assessment ComparisonLaboratory Data:

Boulanger & Idriss 2014:

CRRTX,field ≈ 0.19

CRRB&I ≈ 0.16

CSRB&I ≈ 0.38

Dep

th (m

)

6

1

7

2

8

3

9

4

10

5

CRR & CSR0.2 0.4 0.6

FS ≈ 0.4 – 0.5

Lab or Field FS for Liquefaction Triggering:

Beyzaei et al.

Post-Liquefaction Reconsolidation

TIME (sec)

100 1000 10000

VOLU

MET

RIC

STRA

IN (%

)

0

1

2

3

4

5

EQC4-DM1B-6U-AEQC4-DM1B-6U-BEQC4-DM1B-7U-AEQC4-DM2-3U-AEQC4-DM2-3U-BEQC4-DM2-4U-A

TIME (sec)

100 1000 10000

VOLU

MET

RIC

STRA

IN (%

)

0

1

2

3

4

5

S23-DM1-3U-AS23-DM1-3U-BS23-DM1-4U-BS23-DM1-5U-AS23-DM1-7U-AS23-DM1-7U-BS23-DM1-8Ub-A

Beyzaei et al.

Clean Sand and Silty Sand

Silt (PI=8-10) and Sandy Silt (PI=4-7)

Cyclic Triaxial Test Results

Clean Sand (EQC3-DM1-5U-A)

Non-plastic Silty Sand/Silt (S33-DM1-6U-B)

PI=10 Silt (S33-DM1-8U-A)

Beyzaei et al.

Liquefaction Case Histories

Mostly clean sand sites

Not many silty soil sites

253 cases in total20 cases FC > 35%97 cases (no lab FC)

LiquefactionEffects Observed at Ground Surface

No LiquefactionEffects Observed at Ground Surface

15 cases est. FC > 35%

Boulanger & Idriss (2014) CPT-based method

from Boulanger & Idriss (2014)

R² = 0.6246

0

0.5

1

1.5

2

2.5

3

3.5

4

0 20 40 60 80 100

Ic

Fines Content (%)0.0

1.0

2.0

3.0

4.0

0 20 40 60 80 100I c

Fines Content (%)

Data

R&W(98)-GeneralCorrelation

Ic – Fines Content (FC) Correlations

Robinson, Cubrinovski, & Bradley 2013 CBD Data from Zupan 2014, Taylor 2015, & Markham 2015

Apparent FC


FINES CONTENT (%)0 20 40 60 80 100

SOIL

BEH

AVI

OR

TYP

E IN

DEX

(Ic)

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Site 37 (Logging, S/H)Site 14 (Logging, S/H)Site 33 (Logging, S/H)

BI16 (C_FC=0) BI16 (C_FC=0.2)

Site 2 (CTX, L)Site 14 (CTX, L)Site 21 (CTX, L)Site 23 (CTX, L)Site 33 (CTX, L)

Best-fit (Lab data)

S33-DM1-5U-B

S33-DM1-6U-B

ends mid

top midbot

S/H = Sieve/HydometerL = Laser

Ic – Fines Content Correlation

Closely spaced continuous sampling with thin defined layers (Beyzaei et al.)

Grain-Size Composition of SoilsSand ejecta samples from areas in Christchurch

(Courtesy of M. Pender, Univ. of Auckland)

• Clean fine sands and non-plastic silty sands• Does soil ‘know’ that the #200 sieve exists?

#200

SEM photographs (200x) by Beyzaei et al.

Particle Shape of Soils

Monterey 0/30 sand, FC = 0% S33-DM1-5U-A sand, FC=10%

S23-DM1-8Ub-A silt, FC=63%: coarse fraction (> 75 µm) & fines fraction (< 75 µm)

Importance of Depositional Environment

Recognized but often not explicitly considered

Youd & Perkins (1978): “factors that affect ground failure susceptibility include sedimentation process, age of deposition, geologic history, depth of water table …”

Seed (1979): “method of placement or soil structure” and “age since deposition or placement” “a single layer of relatively impervious fine sand or silt in such a deposit would completely invalidate the results of pore pressure dissipation computations for vertical flow”

Canterbury Plains

Christchurch

Buried Streams in Central Christchurch(from 1850’s ‘Black Maps’)

from M. Cubrinovski

Hereford St.

Armaph St.

Mad

ras

St.

Cathedral

Kilmore St.

from Christchurch: Swamp to City (photo from 1880, 30 years after Christchurch was founded)

Depositional Environment of Silty Sites

RAKAIA RIVER

WAIMAKARIRI RIVER

PORT HILLS

Canterbury Plains

1918 Photo from Christchurch: Swamp to City

Beyzaei et al.

Regional Assessment(a) (b)

Beyzaei et al.

Thin-Layer Stratigraphy:Standard CPT vs. Mini-CPT

Site 33 - Cashmere Site 37 - Clarence

Beyzaei et al.

Site Characterization Tools

qc (MPa)

0 3 6 9 12

DEP

TH B

ELO

W G

RO

UN

D S

UR

FAC

E (m

)

3.65

3.70

3.75

3.80

3.85

3.90

Ic

1 2 3 4

CPT_36421 Mini-CPT_01 Mini-CPT_02

(oxidized)

silt band

organics band

organics band

very fine sand with silt laminations

silt parting

fine sand

silty fine sand

fine sand, some medium sand, trace silt

Graphic Log Sample Photograph

DM High-Quality Sample

(c)

Sonic Boring Core Sample

(b)(a)

Beyzaei et al.

Groundwater Table EffectsCrosshole seismic testing (UT-Austin)Continuous sampling

Piezometer (NZGD)

Site 21

Beyzaei et al.

Over-Estimation of Liquefaction Triggering

Cyclic testing data does not explain the discrepancyOther possible explanations?

• Groundwater table fluctuation & “clayey crust”

• Highly stratified subsurface profile

• At-depth suppression of ejecta movement & reconsolidation time

• Angular particles/borderline soil types

• Inherent conservatism in analysis approach

Combination of all the above?

System Response macro-scale system response as opposed to element/specimen level response

www.engeo.com

Natural Shoal Deposits of Treasure Island, San FranciscoPedro Espinosa, Phil Stuecheli, Stefanos, Papadopoulos, Joe Tootle, Uri Eliahu,

Shah Vahdani, Bahareh Heidarzadeh, Steve Dickenson, Michael Beaty, Juan Pestana, Michael Riemer, Chris Markham, Jonathan Bray, & Nick Sitar

www.engeo.com

ORIGINAL CONDITION, CONSTRUCTION, AND DEVELOPMENT

www.engeo.com

Site Location

Sourced from Google Earth

IMPROVE FILL-SHOAL WITH VIBRO-COMPACTION USING DPC

TEST PROGRAM CPT RESULTS

FillShoal

Full-scale DPC test results indicated that no appreciable densificationcan be obtained within the shoal deposits.

D&M Thin- Walled Piston Sampler

“Undisturbed” Soil Sampling & Testing

ASTM D6519-08

FILL

Fill consists largely of sand and non-plastic silt

SHOAL DEPOSIT

Shoal deposit is heterogeneousnatural deposit often with interlockingsand grains with clay bridges

Close grain packing and clay films bridging pores

Weakly developed clay bridges and few fines in pores

SUBSURFACE GEOLOGY

Silty Soil Liquefaction Effects on Hospital – 2010 Chile EQ (Mw= 8.8)

SILT LIQUEFACTION EFFECTS ON STRUCTURES

1999 Kocaeli, Turkey EQ: Adapazari

Evaluation of Ic < 2.6 CriterionSoils at two sites in Adapazari

Conclusions Loose shallow sand & nonplastic silt deposits led to much

damage in Christchurch, especially in areas with ejecta

Interbedded silty soil sites differ from typical clean-sand sites upon which liquefaction procedures are largely based

Depositional environment distinguishes between sites that did or did not liquefy; CPT-based simplified procedures did not

Understanding “system” response is key

Depositional environment should be explicitly considered in liquefaction assessments. Historical maps, geologic studies, and continuous sampling can provide key information

Silty soil sites could exhibit liquefaction manifestations if heavy buildings were present or if shaken harder

RECOMMENDATIONS

Perform cyclic testing on fine-grained soils that can be sampled effectively to assess their seismic response characteristics.

0

10

20

30

40

50

0.4 0.6 0.8 1.0 1.2 1.4wc/LL

Pla

stic

ity In

dex

Susceptible to LiquefactionModerate SusceptibilityNot Susceptible

Liquefaction triggering procedures, which have been developed for sands and nonplastic silty sands, should be applied with judgment.

Consider depositional environment & system response which may be missed by simplified methods (e.g., thin-layer stratigraphy, & groundwater fluctuations)

seismic performance of silty soil sites - sacramento...

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